Since EMG, ENG and EEG signals are all fundamentally electrophysiological signals, a technique developed to remove stimulus artifact contamination present in any of the biopotential recording, may be modified and used to remove artifact from the other types. These techniques may reduce the effect of stimulus artifact and improve the fidelity of the recorded signals. These stimulus artifacts are due to direct coupling path between the closely spaced electrodes. However, most techniques suffer from an inability to adapt to the dynamic nature of stimulation artifact, due to the non-linearities of the stimulation procedure and hence suffer residual artifact.
Both analog and digital (software-based) techniques have been developed to reduce these artifacts.
An overview of such possible hardware and software techniques have been made in Derek T. O'Keeffe et al. in document “Stimulus artifact removal using a software-based two-stage peak detection algorithm” published in Journal of Neuroscience Methods 109 (2001) 137-145 but all these techniques suggest or reveal a lack of one or two properties to make them widely applicable.
In particular, deep brain stimulation (DBS) is a last resort therapy for drug treatment-resistant neurological diseases such as Parkinson's, obsessive-compulsive disorders, and many more. The classical mm-size electrode solution (e.g. of Medtronic®) supports only weak spatial resolution and is operated in an open-loop stimulation approach only. Such large electrodes usually measure biopotentials averaged on a huge number of electrogenic cells. Such signals present low frequency waves representative of large scale cells activity.
μm-size electrode contacts and both stimulation and recording capabilities provide a better understanding of the actual working principles of DBS, development of new therapies, and in situ monitoring the operation of chronically implanted DBS electrodes.
The use of such μm-size electrode contacts permits the measurement of the action potentials originating from a single electrogenic cell, or from a limited number of cells, so that the action potentials of individual cells can be distinguished.
In such small neural probes, simultaneous stimulation and recording lead to large artifact signals due to direct coupling path between the closely spaced electrodes. Moving to μm-size electrodes worsens the situation. Stimulation signals in the —range of 0.1-to-1 V are superimposed on the neural activity recordings in the 10-to-100 μV range. High-gain analog electronics is required to amplify the weak signals but gets saturated by the high stimulation artifacts. Saturation and recovery from it can result in the loss of recording information over a multiple of the stimulus duration time.